Method of interconnecting subterranean boreholes

ABSTRACT

A method is disclosed of connecting a first borehole to a second borehole, the boreholes being formed in an earth formation and extending at a mutual distance. The method comprises inserting a volume of hardenable fluidic material into a space in the earth formation extending between the first and second boreholes, and allowing the hardenable fluidic material to harden so as to form a body of hardened material between the first and second boreholes. At least one fluid channel is created in the body of hardened material, each fluid channel providing fluid communication between the first borehole and the second borehole.

PRIORITY CLAIM

The present application claims priority from PCT/EP2008/053617, filed 27Mar. 2008, which claims priority from EP Application 07105066.0, filed28 Mar. 2007.

BACKGROUND OF THE INVENTION

The present invention relates to a method of connecting a first boreholeto a second borehole, said boreholes being formed in an earth formationand extending at a distance from each other.

In operations for the production of oil or gas from a subterraneanreservoir at a remote location, such as an offshore location, it isgeneral practice to produce hydrocarbon fluid from one or more wells toa production platform located at the site of the wells. The productionplatform can be fixedly installed on the seabed, such as a jack-upplatform or a gravity based platform, or it can be floating at the seasurface, such as a floating production storage and offloading (FPSO)vessel. Generally, one or more wells are drilled into the reservoir fromdirectly below the platform, and hydrocarbon fluid is produced from thewells through risers extending between the seabed and the platform. Mostoffshore fields also involve one or more satellite wells located at adistance from the platform and tied to the platform by pipelines on theseabed.

Offshore platforms, especially those in deep water, attributeconsiderably to the costs of exploiting offshore hydrocarbon reservoirs.In some instances, installing an offshore platform may even beprohibitive to economical exploitation of the reservoir. In view thereofit has been proposed to use relatively small subsea production systemsinstead of fixed or floating platforms for producing oil or gas fromoffshore fields. Such subsea systems are arranged to receive hydrocarbonfluid from one or more wells to initially separate the produced streaminto a gas stream and a liquid stream, and to pump the separated streamsto an onshore production facility. Alternatively the produced fluids canbe transported in multi-phase flow from the subsea system to an onshorefacility through a single pipeline, hence without initial separation ofgas from liquid.

Although conventional technologies can be applied for the exploitationof some remote hydrocarbon fluid reservoirs, a variety of applicationsrequire improved systems and methods to produce hydrocarbon fluid in aneconomical way. For example, the production of hydrocarbon fluid fromreservoirs located below Arctic offshore waters can prove difficult, ifnot impossible, with conventional technologies. Generally Arcticconditions prohibit continued operation of offshore facilitiesthroughout the year, for example because the sea is frozen a large partof the year. For this reason, conventional offshore drilling and/orproduction platforms are considered inadequate for continued operationthroughout the year in Arctic conditions. Moreover, exposure ofpipelines to scouring from floating ice and/or hazards associated withunstable permafrost, can be prohibitive.

US patent application 2004/0079530 A1 discloses a method ofinterconnecting subterranean boreholes, whereby a first borehole extendsinto an offshore hydrocarbon reservoir, and whereby a second borehole isdrilled from a surface location horizontally displaced from the surfacelocation of the first borehole such that a lower, substantiallyhorizontal, section thereof intersects the first borehole to providefluid communication between the first and second boreholes.

A problem of the known method of interconnecting subterranean boreholesrelates to the difficulty to drill the second borehole such that itintersects the first borehole. Moreover, the two boreholes can beunaligned at the point of intersection so that it becomes difficult, orimpossible, to install a liner at the location of the intersection.Also, the two boreholes may have to be drilled at an undesirably highinclination angle relative to each other to create the intersection.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide an improved methodof interconnecting first and second boreholes formed in an earthformation, which method overcomes the problems of the prior art.

In accordance with the invention there is provided a method ofconnecting a first borehole to a second borehole, said boreholes beingformed in an earth formation and extending at a mutual distance, themethod comprising:

inserting a volume of hardenable fluidic material into a space in theearth formation extending between the first and second boreholes, andallowing the hardenable fluidic material to harden so as to form a bodyof hardened material between the first and second boreholes; and

creating at least one fluid channel in said body of hardened material,each fluid channel providing fluid communication between the firstborehole and the second borehole.

With the method of the invention it is achieved that there is no longera need to drill the boreholes exactly so that one borehole intersectsthe other borehole. Moreover it is achieved that there is no abruptchange of direction of the boreholes at the location where theconnection is made, so that a liner (or casing) can be installed moreeasily at said location. Also, due to the relative hardness of the bodyof hardened material, there is a reduced risk of erosion at the locationof the connection during continued production of hydrocarbon fluidthrough the fluid channel(s) formed therein.

Suitably, said space provides fluid communication between the firstborehole and the second borehole. For example, said space can include aplurality of pores of the earth formation.

In a preferred embodiment, the method of the invention comprisescreating a cavity in the earth formation, said cavity forming at least apart of said space.

To reduce the size of the cavity, suitably the cavity extends between aselected location of the first borehole and a selected location of thesecond borehole, and wherein said mutual distance of the boreholes isminimal from the selected location of the first borehole to the selectedlocation of the second borehole.

An exemplary way of creating the cavity in the earth formation, is tocreate at least one flow passage in the earth formation, each flowpassage providing fluid communication between the first borehole and thesecond borehole. Such flow passage can be created, for example, byperforating the earth formation using a shaped charge. To enlarge thediametrical size of the flow passage, suitably fluid is induced to flowthrough the flow passage so as to erode the earth formation surroundingthe flow passage to form the cavity.

Each fluid channel is preferably formed by perforating the body ofhardened material.

In an advantageous embodiment of the method of the invention, the firstborehole extends into a reservoir zone of the earth formation containinghydrocarbon fluid. Suitably the reservoir the first borehole extendssubstantially parallel to a boundary of the reservoir zone.

To prevent an undesired high drawdown of reservoir fluid at the locationof the connection of the two boreholes, it is preferred that the firstborehole is provided with a liner passing from outside the body ofhardened material to within the body of hardened material.

The hardenable material can be selected, for example, from cement andresin such as a phenolic-based thermoset plastic resin.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described hereinafter in more detail and by way ofexample, with reference to the accompanying drawings in which:

FIG. 1 schematically shows an embodiment of two wellbores interconnectedwith the method of the invention;

FIG. 2 schematically shows a detail of the embodiment of FIG. 1;

FIG. 3 schematically shows cross-section 3-3 of FIG. 2 during an initialstage of the method of the invention;

FIG. 4 schematically shows cross-section 3-3 of FIG. 2 during asubsequent stage of the method of the invention;

FIG. 5 schematically shows cross-section 3-3 of FIG. 2 during a furtherstage of the method of the invention;

FIG. 6 schematically shows cross-section 3-3 of FIG. 2 during a finalstage of the method of the invention; and

FIG. 7 schematically shows cross-section 7-7 of FIG. 6.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring initially to FIG. 1, there is shown a first wellbore 1 and asecond wellbore 2 formed in an earth formation 3 that includes areservoir zone 4 containing hydrocarbon fluid. First wellbore 1 extendsfrom a drilling rig 6 at surface into the earth formation 3 such that alower section 8 of the first wellbore 1 extends inclined into thereservoir zone 4. Second wellbore 2 extends from a hydrocarbon fluidproduction facility 9 at surface into earth formation 3 whereby a lowersection 10 of the second wellbore extends substantially horizontally, ordeviated, into reservoir zone 4. Lower sections 8, 10 of the respectivefirst and second wellbores 1, 2 do not directly intersect each other,but extend at a distance from each other whereby the shortest distancetherebetween is about one or several meters. The area in which first andsecond wellbores 1, 2 cross each other, is indicated by reference sign‘A’.

The area ‘A’ is shown in more detail in FIGS. 2 and 3, wherein FIG. 3 isa cross-sectional view taken along line 3-3 of FIG. 2. First wellbore 1is provided with a casing 12 extending to about the bottom of wellbore1, and second wellbore 2 is provided with a liner 14 extending in lowerwellbore section 10. Liner 14 has a plurality of inlet openings (orperforations) 16 to allow hydrocarbon fluid from the reservoir zone 4 toflow into liner 14. However a portion 18 of liner 14 extending nearfirst wellbore 1 is solidly formed, that is, the liner portion 18 is notprovided with inlet openings (as shown in FIG. 2). Furthermore, aportion of casing 12 nearest second wellbore 2 is provided with aplurality of primary perforations 20. Primary perforations 20 extendfurther through the earth formation surrounding casing 12 and liner 14so as to provide fluid communication between wellbore 1 and wellbore 2.

In FIG. 4 is shown the area ‘A’ after a cavity 22 has been formed in theearth formation. Cavity 22 encloses a portion of liner 14 and extends tocasing 12, at the location thereof where primary perforations 20 areformed.

In FIG. 5 is shown the area ‘A’, in the view along line 3-3 of FIG. 2,after cavity 22 has been filled with a body of cement 24 or othersubstantially impermeable material.

In FIGS. 6 and 7 is shown the area ‘A’ after a series of secondaryperforations 26 have been formed in casing 12, which extend furtherthrough the body of cement 24 and liner 14 so as to provide fluidcommunication between wellbore 1 and wellbore 2.

During normal operation, first wellbore 1 is drilled such that the lowersection 8 thereof crosses lower section 10 of second wellbore 2 at arelatively short distance, for example a distance between 0.2-2 meters.A perforating gun (not shown) may then be lowered into first wellbore 1and operated so as to form primary perforations 20 which extend throughcasing 12, earth formation 3 and liner 14 so as to provide fluidcommunication between first wellbore 1 and second wellbore 2 (as shownin FIGS. 2 and 3).

In a subsequent step, a stream of liquid, such as brine or drillingfluid, is pumped from surface into the first wellbore 1. The stream ofliquid passes into the lower wellbore section 8, and flows from therevia the primary perforations 20 into the lower section 10 of the secondwellbore 2. The stream of liquid is then discharged from the secondwellbore 2 through the surface production facility 9. The stream ofliquid flows at high velocity through the primary perforations 20 andthereby erodes the rock material around the perforations 20. Uponcontinued pumping of the stream of fluid, virtually all rock materialaround the primary perforations 20 erodes away so that, as a result, thecavity 22 is formed in the earth formation 3 (as shown in FIG. 4).

During a next phase, cement is pumped into the lower section 8 of thefirst wellbore 1, and thence via the primary perforations 20 of thecasing 12 into the cavity 22. Upon hardening of the cement, the body ofhardened cement 24 forms in the cavity 22 (as shown in FIG. 5).

A perforating gun (not shown) is then lowered into the first wellbore 1and operated so as to form the secondary perforations 26 which extendthrough the casing 12, the body of hardened cement 24, and the liner 14so as to provide fluid communication between the first wellbore 1 andthe second wellbore 2 (as shown in FIG. 6).

The sets of primary perforations 20 and the sets of secondaryperforations 26 can be shot with the same perforating gun, however itmay be preferred to use different perforation guns depending on thehardness of the rock to be penetrated (for the primary perforations 20)and the hardness of the cement to be penetrated (for the secondperforations 26).

Alternatively, a suitable abrasive jetting tool may be used to createthe primary perforations and/or the secondary perforations by jetting afluid stream containing abrasive particles against the rock formationand/or the body of cement.

In this manner it is achieved that hydrocarbon fluid produced from thereservoir zone 4, can flow from the second wellbore 2 to the firstwellbore 1, or vice versa, via the secondary perforations 26. Forexample, if the second wellbore 2 extends below the sea, and the firstwellbore 1 extends to an onshore surface location, produced hydrocarbonfluid can flow from the lower section 10 of the second wellbore 2, viathe secondary perforations 26, into the lower section of the firstwellbore 1 and from there to the onshore surface location. Also, bothwellbores can be formed below the seabed.

It should be noted that, by virtue of the absence of inlet openings inthe liner, hydrocarbon fluid can only flow into the liner 14 at somedistance from the body of cement 24. It is thereby achieved thatundesired high drawdown of hydrocarbon fluid from the reservoir zone 4in the region near the body of cement 24, is prevented.

Instead of pumping cement into the cavity, a hardenable resin can bepumped into the cavity. Upon hardening of the resin, a body of hardenedresin is formed in the cavity, whereafter the secondary perforations areformed in the body of hardened resin.

1. A method of connecting a first borehole to a second borehole, saidboreholes being formed in an earth formation and extending at a mutualdistance, the method comprising: inserting a volume of hardenablefluidic material into a space in the earth formation extending betweenthe first and second boreholes, and allowing the hardenable fluidicmaterial to harden so as to form a body of hardened material between thefirst and second boreholes; and creating at least one fluid channel insaid body of hardened material, each fluid channel providing fluidcommunication between the first borehole and the second borehole.
 2. Themethod of claim 1, wherein said space provides fluid communicationbetween the first borehole and the second borehole.
 3. The method ofclaim 1, wherein said space includes a plurality of pores of the earthformation.
 4. The method of claim 1, further comprising creating acavity in the earth formation, said cavity forming at least a part ofsaid space.
 5. The method of claim 4, wherein the cavity extends betweena selected location of the first borehole and a selected location of thesecond borehole, and wherein said mutual distance of the boreholes isminimal from the selected location of the first borehole to the selectedlocation of the second borehole.
 6. The method of claim 4, wherein thestep of creating said cavity in the earth formation comprises creatingat least one flow passage in the earth formation, each flow passageproviding fluid communication between the first borehole and the secondborehole.
 7. The method of claim 6, wherein the step of creating said atleast one flow passage comprises perforating the earth formation.
 8. Themethod of claim 6, further comprising inducing fluid to flow througheach flow passage so as to erode the earth formation surrounding theflow passage to form the cavity.
 9. The method claim 1, wherein saidhardenable material is selected from cement and resin.
 10. The methodclaim 1, wherein the step of creating said at least one fluid channelcomprises perforating the body of hardened material.
 11. The method ofclaim 1, wherein the first borehole extends into a reservoir zone of theearth formation containing hydrocarbon fluid.
 12. The method of claim11, wherein the reservoir zone has a boundary, and wherein the firstborehole extends substantially parallel to said boundary.
 13. The methodof claim 11, wherein the second borehole extends to the earth surface.14. The method of claim 1, further comprising arranging a liner in thefirst borehole, the liner passing from outside the body of hardenedmaterial to within the body of hardened material.
 15. A wellbore systemcomprising first and second boreholes formed in an earth formation, saidboreholes being connected to each other using the method of claim
 1. 16.(canceled)